This invention relates to standby operation of a fuel cell power plant which generates electric power using a reformate gas.
Tokkai Hei 8-306379 published by the Japanese Patent Office in 1996 discloses standby operation of a fuel cell power plant which generates power in a fuel cell stack using a reformate gas.
According to this prior art, when power supply by the fuel cell power plant is not required, the fuel cell power plant is operated to achieve an output of 25-30% of a rated output. This output is used to electrolyze water in order to produce hydrogen. The resulting hydrogen is re-supplied to the fuel cell stack.
Due to this low-output standby operation, when power supply is required, rated operation of the fuel cell power plant can be rapidly established. Furthermore, since hydrogen produced during the standby operation is re-supplied to the fuel cell stack, consumption of reformate gas during standby operation can be maintained at low levels.
When electrolyzing water, supply of water must be ensured. When the fuel cell power plant is mounted in a vehicle, a water supply device has also to be installed in the vehicle. However, it is difficult to ensure a space for the water supply device with a water tank in the vehicle.
As a result, in a vehicle-mounted fuel cell power plant, it is preferred that water is not electrolyzed and low-output standby operation with only the aim of maintaining the temperature of the fuel cell stack is performed.
In a fuel cell power plant using a reformer to generate a reformate gas by partial oxidation, the temperature of the reformate gas is controlled by the amount of air supplied to the reformer. During standby operation in order to maintain the temperature of the fuel cell stack, the amount of air supplied to the reformer is conspicuously lower than during rated operation. The air supply amount is generally controlled using a valve. However problems arise in maintaining control accuracy of the valve throughout the wide range from the minute flow amounts above to the high flow amounts during rated operation.
It is therefore an object of this invention to realize standby operation adapted to a fuel cell power plant mounted in a vehicle.
In order to achieve the above object, this invention provides a fuel cell power plant comprising a fuel cell stack generating power using a hydrogen-rich gas, a hydrogen-rich gas generating mechanism which produces a hydrogen-rich gas by an exoergic reaction of a vaporized fuel and air, a first air supply passage which supplies air to the hydrogen-rich gas generating mechanism, a second air supply passage which supplies air to the hydrogen-rich gas generating mechanism, and a cut off valve which cuts off the first air supply passage. The second air supply passage is set to have a smaller cross sectional area than the first air supply passage.